1. Field of the Invention
The present invention relates to a noncontact ophthalmotonometer used to measure pressure of an eye to be examined at an ophthalmic hospital or the like.
2. Description of the Related Art
Hitherto, in a noncontact ophthalmotonometer, pressure required to deform a cornea by a predetermined amount is determined by blowing fluid onto an eye to be examined in order to measure pressure of the eye to be examined from the determined required pressure.
In such a noncontact ophthalmotonometer, in order to achieve precise measurement, a gap between a nozzle, mounted to the central portion of an optical member, and the vertex of the cornea of the eye to be examined needs to be precisely provided.
Conventionally, a method of aligning a noncontact ophthalmotonometer with respect to an eye to be examined by operation of a joystick or upper and lower rings by an examiner and a method of aligning a noncontact ophthalmotonometer in which, as disclosed in Japanese Patent Laid-Open No. 8-10225, the noncontact ophthalmotonometer automatically precisely aligns itself with an eye to be examined after an examiner has performed an aligning operation by a certain amount have been proposed.
In a noncontact ophthalmotonometer, since the distance between the nozzle and the vertex of a cornea is short, a stopper is provided as a safety device to prevent the nozzle from coming closer to an eye to be examined than a certain distance, so that the nozzle does not come into contact with the eye to be examined. After a subject has placed his chin onto a chin support, the examiner moves the noncontact ophthalmotonometer towards the eye to be examined while looking through it from beside it. When the examiner judges that the noncontact ophthalmotonometer has reached a limit as to how close it can be moved towards the eye to be examined, the stopper operates.
However, in the conventional method in which an examiner performs an aligning operation, a considerable amount of time is required to complete measurements depending on how skilled the examiner is, thereby placing a burden on the subject.
Even if a noncontact ophthalmotonometer is made capable of aligning itself to an optimal position after an examiner has aligned it to a position near the optimal position, it is still necessary for the examiner to align the noncontact ophthalmotonometer to a position near the optimal position. Thus, the level of skill required to align the noncontact ophthalmotonometer has not been adequately lowered.
As regards the safety device, even if the stopper is set prior to carrying out measurements, when a subject moves his head after the stopper has been set, it is necessary to reset the stopper, so that the measurements become more troublesome and time-wasting.